In conventionally known suction apparatuses for holding a material to be suctioned such as a wafer or other substrate by vacuum-suctioning the material to be suctioned, a rigid suction substrate comprising a plurality of pin-like or ridged protrusions of which the tip-end faces thereof are the same height is formed on the side of the suction apparatus to which the material to be suctioned is suctioned (for example, Japanese Unexamined Patent Application Publication Nos. 2002-217141 and H10-50810).
In these suction apparatuses, a negative pressure is created in depressions between the protrusions in a state in which the tip-end faces of the protrusions are in contact with a wafer to ensure the wafer is held planarly against the tip-end faces of the protrusions. A suction surface where the tip-end faces of the protrusions are held in contact with the wafer is established in the suction apparatus in this way.
When a foreign material becomes interposed between the wafer and the suction surface of the suction apparatus, the wafer deforms and forms a bulge in proximity of the location of the foreign material that, in turn, results in various undesirable outcomes. For example, when polishing is performed to planarize the wafer, excessive polishing will occur in the location in which the bulge has been produced by the foreign material and will result in a fatal defect thereof. Although the wafer and the suction surface of the suction apparatus are normally washed, it is impossible to completely remove such foreign materials.
Because the contact surface area between the wafer and the suction surface is limited to the surface area of the tip-end faces of the protrusions in the aforementioned conventional suction apparatuses disclosed in Japanese Unexamined Patent Application Publication Nos. 2002-217141 and H10-50810, a highly desirable marked reduction in the probability of a foreign material such as dust or polishing agent becoming interposed between the wafer and the suction surface is afforded thereby.
Although the contact surface area between the wafer and the suction surface of the aforementioned conventional suction apparatuses disclosed in Japanese Unexamined Patent Application Publication Nos. 2002-217141 and H10-50810 can be regarded as small, the possibility that a foreign material will become interposed therebetween cannot be completely eliminated. When a foreign material becomes interposed between the wafer and the tip-end faces of the protrusions in the aforementioned conventional suction apparatuses, as described above, the wafer deforms and forms a bulge in proximity of the location of the foreign material which, in turn, results in various undesirable outcomes.
Japanese Unexamined Patent Application Publication No. 2004-259792 proposes an elastic layer affixed to the tip-end faces of the aforementioned protrusions. More specifically, a non-woven fabric of thickness of the order of several hundred μm is employed as the aforementioned elastic layer and is adhered to the tip-end faces of the protrusions using a double-side adhesive tape. A case in which the aforementioned non-woven fabric is arranged on the tip-end faces only of the aforementioned protrusions (FIG. 1 of Japanese Unexamined Patent Application Publication No. 2004-259792), and a case in which the aforementioned non-woven fabric is connectively formed in an overall sheet-like shape and laid across the top of the depressions between the aforementioned protrusions and in which a plurality of through-holes that afford through-connection of the aforementioned depressions to the side of the material to be suctioned that is suctioned are formed in the aforementioned non-woven fabric (FIG. 7 of Japanese Unexamined Patent Application Publication No. 2004-259792) have been proposed.
If a foreign material such as dust becomes interposed between the suction-held wafer and the aforementioned elastic layer when the aforementioned elastic layer has been affixed to the top of the tip-end faces of the aforementioned protrusions in this way, because the foreign material attempts to embed itself in the aforementioned elastic layer due to the elasticity of the aforementioned elastic layer, the bulge in the wafer in proximity of the location of the foreign material is comparatively less than when there is no aforementioned elastic layer provided and, to that end, the planarization of the suction-held wafer can be improved.
However, in the aforementioned conventional art proposed in Japanese Unexamined Patent Application Publication No. 2004-259792, because a double-sided tape is used to adhere the non-woven fabric to the top of the tip-end faces of the protrusions, a comparative increase in the thickness of the non-woven fabric of several hundred μm is unavoidable. However, it is apparent that when a condition in which different pressure is applied to the various areas of the non-woven fabric (this condition is generated by, for example, relative movement between the wafer and the polishing pad during polishing performed to planarize the wafer.) arises when the thickness of the non-woven fabric is made comparatively thicker in this way, comparatively greater differences in the thickness of the various areas of the non-woven fabric are produced and, originating therein, undulations are produced in the wafer that, in turn, lead to lowering of the planarization of the wafer.
In addition, in the aforementioned case depicted in FIG. 7 of Japanese Unexamined Patent Application Publication No. 2004-259792 of the aforementioned conventional art proposed in Japanese Unexamined Patent Application Publication No. 2004-259792, it is apparent that because the non-woven fabric is connectively formed in an overall sheet-like shape and laid across the top of the depressions between the protrusions and a plurality of through-holes that afford through-connection of the aforementioned depressions to the side of the material to be suctioned which is suctioned are formed in the aforementioned non-woven fabric, undulations are generated in the regions in which the non-woven fabric is laid across the depressions between a location in proximity of the aforementioned through-holes on which a suction force has action and the remaining locations and, originating therein, undulations are produced in the wafer that, in turn, lead to lowering of the planarization of the wafer. Also, in the aforementioned case depicted in FIG. 1 of Japanese Unexamined Patent Application Publication No. 2004-259792, while there is an absence of undulations generated in the wafer for the reason that the non-woven fabric is arranged only in the tip-end faces of the aforementioned protrusions, arrangement of the non-woven fabric in the tip-end faces only of the aforementioned protrusions is, from the manufacturing standpoint, very difficult to implement in actual practice.
As is described above, in the aforementioned conventional art proposed in the aforementioned Japanese Unexamined Patent Application Publication No. 2004-259792, irrespective of whether or not the generation of bulges in the wafer in proximity of the location of a foreign material can be reduced by provision of a non-woven fabric and, in turn, the planarization of the wafer can be improved, the planarization of the wafer can be lowered for a reason originating in the non-woven fabric that is unrelated to the presence of a foreign material.
While the description provided above pertains to an example in which the material to be suctioned is a wafer, the same applies to other materials to be suctioned.